According to the United States Cancer Statistics: 2005 Incidence and Mortality report provided by the Centers for Disease Control and Prevention, colorectal cancer is the third leading cause of cancer death among men and women in the United States. The identification of suspicious polyps in the colonic lumen may be a critical first step in detecting the early signs of colon cancer. Many colon cancers may be prevented if precursor colonic polyps are detected and removed.
Computed tomographic (CT) and magnetic resonance (MR) colonography, two non-invasive or “virtual” procedures for imaging the colonic lumen, have emerged as alternatives to the invasive optical colonoscopy procedure, which has traditionally been considered the gold standard for viewing the colon. CT imaging systems, for example, may acquire a series of cross-sectional images (i.e., slices) of the abdomen using scanners and x-rays. Computer software may be used to construct additional imagery from the slices. Physicians may inspect the imagery for indicators of colonic polyps. Recently, physicians have used computer-assisted analysis to inspect virtual colonography medical imagery and identify suspicious colonic polyps. Also known as computer-aided detection or “CAD,” it has been demonstrated that physicians who use a CAD system as a “second set of eyes” benefit significantly, either by increased sensitivity and/or by reduced interpretation time. (See, for example, “Computed tomographic colonography: assessment of radiologist performance with and without computer-aided detection,” Halligan et al., Gastroenterology, 131 (6). pp. 1690-1699.)
In a clinical setting, it is common practice to image the colon while a patient lies in multiple positions. For example, a patient's colon may be imaged while a patient lies in the prone (i.e., face down) and supine (i.e., face up) positions. Studies suggest that use of both the supine and prone positions for patients undergoing virtual colonography improves evaluation of the colon and increases sensitivity for polyp detection. (See, for example, “CT colonography: value of scanning in both the supine and prone positions,” American Journal of Roentgenology, 1999 March; 172(3):595-599.) As virtual colonography procedures gain wider acceptance, it will also be increasingly common practice to image the colon of a patient at substantially different times (e.g., 5 or 10 years apart) to analyze changes. Typically, the multiple views of the colon are separately analyzed by a CAD system for suspicious anomalies and separately reviewed by a physician. Unfortunately, a high number of false positives are frequently detected in each view, which is undesirable to the physician or other user of the CAD system.
Prior art CAD systems and methods such as those described in U.S. Pat. No. 6,075,879, “Method and system for computer-aided lesion detection using information from multiple images,” assigned to R2 Technology, Inc; and “Region-based supine-prone correspondence for the reduction of false-positive CAD polyp candidate in CT Colonography,” Academic Radiology, Vol. 12, No. 6, June 2005, may analyze suspicious anomalies using information from multiple views. However, those systems and methods may assume that if suspicious anomalies appear in multiple images of an anatomical region of interest, they are more likely to be of interest to the physician. Unfortunately, many polyp-like false positives will persist across multiple volumes of a colon and are not eliminated using these prior art CAD systems and methods. Furthermore, many polyps will often be detectable in only one view of the colon and may be wrongly dismissed using these prior art CAD systems and methods.
It is therefore an object of this disclosure to overcome both the aforementioned and other limitations associated with prior art approaches in which information from multiple medical images is used to improve the automatic identification of suspicious anomalies in an anatomical colon.